The rapid advances in microprocessor technology in recent years have resulted in the application of this technology in many consumer product areas. In the area of power tools, for example, microprocessor systems can be used to control or monitor such functions as the position of the tool with respect to the workpiece and the speed of the tool with far greater accuracy than could heretofore be achieved.
Microprocessor technology has been found to be particularly suitable for application in such tools as drill presses and similar devices wherein accurate monitoring and control of the output speed and depth of entry into the workpiece of the tool are particularly important. However, tools of this type often achieve a relatively broad range of output speeds by use of multiple gear ratio mchanisms, most commonly a dual gear ratio system wherein a desired output speed may be selected from first and second output ranges corresponding to first and second gear ratios. It is well known to those skilled in the art that the use of a lower drive to driven gear ratio will produce a slower, higher torque output, suitable for heavy duty work, whereas a high drive to driven gear ratio will produce a higher speed, lower torque output, suitable for lighter work.
Generally, shifting of gear ratios is a mechanical function, independent of the electronic, microprocessor system. Although the shifting function could be achieved electrically, this would add substantial circuitry and cost to the unit. Therefore, mechanical, manual shifting has been found preferable. Howver, as the manual gear shifting mechanism is operated independently of the electrical system, means must be provided to enable the electrical, microprocessor control to distinguish between gear ratio engagements in order to compute output speed as a function of armature speed and to effect speed selection and control from the selected range.
Therefore, significant benefits would be achieved by providing a mechanical gear selection system with indicator means for communicating the gear selection to the microprocessor speed selection and control system. Further advantages would be achieved by providing an indicator system which is simple and inexpensive to produce, which is reliable and which is not prone to mechanical failure or human error.